The present invention concerns a multilayer, pleatable, filter material comprising of at least one melt-blown, fleece layer and at least one carded, fleece layer that are attached to one another without use of adhesives for filtering solid particles out of fluids, in particular, filtering solid particles out of gases.
Modern filter materials of the type in question are subject to various demands, such as employment of a single type of material only, economical manufacture, ready processability, even during folding, adequate mechanical stability during use, maximum attainable airflow rates that are adequate for their intended purposes, combined with efficient filtration, and high capacities for storing dust, i.e., long service lives.
European Patent Application EP 0910454 B1 describes a particle filter in the form of a pleated, laminar, fleece material employed as a room-air filter or an air filter for the interiors of motor vehicles. An unsupported, monolayer, microspun, bonded fleece having a greater fiber density at its downstream face than at its upstream face was proposed as the filtration medium. However, such a monolayer material provides only a low dust-storage capacity; i.e., in the case of monolayer media, longer service lives may be achieved only at the expense of filtration efficiency.
German Patent Application DE 19920983 C2 depicts duolayer or multilayer filtration media for filtering air that employ, for example, star-folded cartridges, pleated panel filters, minipleated cassettes, or flat-panel filters, as filter elements for filtering solid matter out of gases. A coarse, melt-blown layer, whose pores are larger than those of the succeeding layer is situated on the upstream face of the duolayer or multilayer filtration medium. An additional process for attaching the individual layers to one another, for example, by means of ultrasonic welding, thermal welding, or application of adhesives, is required in order that the layers will not shift during pleating. Due to the time and effort involved in their manufacture, such products are expensive, and have thus failed to penetrate the market.
World Patent Application WO 98/52672 A1 describes a pleatable, laminated, composite fleece for use as a filtration medium on automotive air filters. That filtration medium is composed of a high-bulk, fiber mat consisting of staple fleece fibers that has a fiber-density gradient extending across its cross-section, a spun-fleece layer laminated thereto, and a stiffening cover layer. The lamination necessitates an additional processing stage, and the employment of adhesives may cause accumulations of dust in the vicinities of the interfaces of adjacent fleece layers that could block flow through the filter.
German Patent Application DE 20207663 U1 depicts a multilayer-filter assembly for filtering dust out of fluids that comprises a coarse-dust-filtration layer, a fine-dust-filtration layer, and a supporting layer and has a gradient, i.e., fibers whose diameter continuously decreases from the coarse-dust-filtration layer to the fine-dust-filtration layer. Such multilayer-filter assemblies are employed as pouch-type filter bags, pleated filters on filter cassettes for industrial dust filtration, automotive air filters, or large-area exhaust filters on home dust-filtration devices. These types of filters have at least three layers, and are thus more expensive to manufacture.
A pleated filter consisting of a fleece having an assortment of thermoplastic fibers having differing diameters that is laminated onto either a microporous membrane, a porous glass-fiber material, or a long-fiber fleece is known from European Patent Application EP 0904819 A1. However, this type of filter has the disadvantage that it is constructed from various types of materials, which makes disposing of used filters problematical.
German Patent Application DE 19953717 C2 discloses a fluid-permeable, microfiber mat that consists of at least one layer, and is employed in the particulate-filtration field as a filtration medium in the manufacture of filter pouches, planar filter inserts, or folded filter inserts for use on filter cartridges or cassettes. In the event that high filtration efficiencies, combined with high dust-storage capacities, are demanded, they may be achieved only by overlaying several layers of these fiber mats, in which case, the manufacturing process will, once again, be extremely time-consuming and expensive.